Oxygenated derivatives of arachidonic acid (AA) produced by inflammatory cells act as potent mediators of inflammation and allergy. This study proposes: 1) that vegetarians who consume little preformed AA have lower AA in serum and cellular complex lipids; and 2) dramatic reductions in serum and cellular AA levels as well as eicosanoid biosynthesis can be achieved when AA and its metabolic precusors, such as linoleic acid, are largely removed from diets of omnivore volunteers.